1. Field of the Invention
The present invention relates to an optical disk for recording copyrighted content information, and a method and an apparatus for reproducing copyrighted content information recorded in an optical disk.
2. Description of the Related Art
In recent multimedia societies, optical disks such as a CD-ROM and a DVD have become remarkably widespread. With the widespread use of the optical disks, so-called pirated ROM disks have appeared and allow a pirate to benefit from the disk without compensating a copyright owner by fraud by illegally making a pirated copy of the optical disk. The percentage of pirated copies of disks is rapidly increasing. Illegal copying of the optical disk can take place in the following manner. Generally speaking, a pirate purchases an authorized optical disk, makes a master tape by reproducing information recorded on the optical disk by means of a disk drive, and mass-produces the pirated copies from the master tape by the same method as a general disk manufacturing method.
In order to protect against the above-mentioned unauthorized copying, some optical disks are devised so that they can be reproduced by only a player designed specifically for them. As this type of optical disk, for example, there is disclosed in the Japanese Patent Laid-Open Publication No 7-85574 a method including the steps of recording main information on an optical recording medium using a predetermined coding means, storing key information indicating decoding means for decoding the main information in a form of a barcode symbol in a mirror surface area or the like, reading our the key information by a reproducing apparatus, decoding and reproducing the main information utilizing a coding method indicated by the key information.
The above-mentioned method of protecting against unauthorized copying has such a very excellent advantage that a general optical disk player cannot reproduce the optical disk. However, the method is helpless against and cannot protect against copying means for performing copying involving no reproducing operation, i.e., for physically copying or transferring concavo-convex pits of data of a signal recorded on an optical disk surface as they are. This copying method requires no reproducing means, and can copy concavo-convex pit information of the optical disk as it is even though original data of signal to be recorded on the optical disk is made sophisticated and complicated. Therefore, the above mentioned method of protecting against unauthorized copying is useless.